ENH: handle entry alternatives outside of string expansion

- string expansions have supported "${var:-default}" syntax for
  several versions, but this did not apply plain dictionary expansions.

  Eg, the following did not parse

     massFlow  ${entry1:-100};

ENH: remove content and length restriction on '${..}' quoted variables

- allows this type of content:

     velocity2  ${velocity1:- ( 0 -100 10) };

- accept empty parameter strings for entries. This allows the
  following expansion to work as expected:

      hex (n1 n2..)  ${inletBlock:-} (10 10 10) simpleGrading (1 1 1)

  ie, optionally define the cellZone name for a given block

ENH: add single parameter dictionary writeEntry method.

- the dictionary knows its own name (dictName), which can be used
  when writing content